>-----Original Message----- >From: Adam Jackson [mailto:a...@redhat.com] >Sent: Friday, February 21, 2020 11:33 PM >To: Yin Shiyou; pixman@lists.freedesktop.org >Subject: Re: [Pixman] [PATCH v2 2/3] build: use '-mloongson-mmi' for Loongson >MMI. > >On Thu, 2020-02-20 at 22:23 +0800, Yin Shiyou wrote: >> It's suggested to use '-mloongson-mmi' to enable MMI. >> To keep compatible with old processor, '-mloongson-mmi' will be >> setted for Loongson-3A only. > >The pattern we've used for other CPUs is to build support for as many >ISA extensions as possible, unless they are explicitly disabled. >Distributions tend to want to set their own minimum ISA levels, and if >they wanted to assert -mloongson-mmi they would already have added it >to CFLAGS globally. > >Do you have any performance data for this change? > >If setting -mloongson-mmi means the compiler can do useful >autovectorization, then that's probably true for other arches too (eg >amd64 vs avx2), and we should support this kind of thing more >generically. But as it stands I don't think this patch is a good idea. > First, that's introduce the history of '-march=loongson2f' and '-mloongson-mmi'. >From loongson2f start, mmi is supported by loongson processor. Unfortunately, the compiler's support for MMI extention is not standardized. Gcc compiler use '-march=loongson2f' for loongson2f at first, but from Loongson-3A, opcode of mmi instruction has changed, and '-march=loongson3a' is in replaced. >From last year, compile option for mmi instruction has been standardized. Just like -mmsa for mips MSA. (MMI,LSX,LASX is Loongson SIMD extention.) -mloongson-mmi for MMI (-march=loongson3a still works, but -mloongson-mmi is recommended for new processors except Loongson2f. ) -mloongson-sx for LSX -mloongson-asx for LASX
Second, back to this patch itself. I meet a problem when compile pixman on my Loongson3a with gcc, MMI can't be enabled. configure check failure: " linking mips:loongson_2f module with previous mips:gs464 modules" It can be solved by assign LS_CFLAGS="-mloongson-mmi" while config. So I submit this patch in hope that no need to assign LS_CFLAGS explicitly. This won't have much impact on performance as I know. Third, about the compatibility with Loongson2f. This patch does not change the result of pixman compilation and running on loongson2f. Before add this patch, LS_CFLAGS will be setted as '-march=loongson2f' by default, After add this patch, LS_CFLAGS is still setted as '-march=loongson2f' if we compile on the old environment. It only makes MMI can be enabled without assign LS_CFLAGS explicitly while compiling locally on loongson-3A. _______________________________________________ Pixman mailing list Pixman@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/pixman
